1. Technical Field
The invention relates generally to integrated circuit (IC) chip fabrication, and more particularly, to a method, system and program product for bonding two circuitry-including substrates, and a related stage.
2. Background Art
In the semiconductor device fabrication industry, three dimensional integration (3DI) techniques may be used for integration at the component level as a packaging process or at the device/circuit level. Device/circuit level 3DI includes the combining of different substrates (i.e., wafers), each having patterned circuitry formed thereon, in a manner to form a larger device/circuit by matching appropriate circuit parts together. More specifically, two substrates are placed in contact with each other in an aligned manner, and pressure is applied to initiate the bonding of the two substrates. In conventional non-patterned substrate bonding (i.e., no circuitry matching performed), the alignment between the two starting substrates is not critical, as it requires only general alignment (e.g., notch-to-notch) with typical alignment accuracy of approximately 5 μm. However, for device/circuit level 3DI applications, the alignment between the two substrates becomes critical due to the circuit connections that need to be made between the patterned circuitry within each substrate. The better the bonding alignment capability, the less misalignment tolerance that needs to be built into circuit designs and therewith the silicon area used for the integrated circuit
A major challenge to advancement of device/circuit level 3DI is obtaining enough accuracy to enable stacked structures in the front-end-of-line (FEOL), i.e., processing performed on the semiconductor substrate in the course of device manufacturing up to first metallization. Currently, the 3DI alignment industry is limited to 1.0 um to 1.5 um alignment accuracy. Attempts at obtaining sub-micron accuracy show that, as alignment capability improves in terms of better control of rotation and translation in a lateral (X and Y) direction, differences in substrate materials such as material thermodynamics, flatness, etc., become major contributors to misalignment. One approach to one of these issues, flatness, has been to provide piezo-electric actuators in a stage to which a substrate is attached to provide mechanical corrections in a surface of the substrate. Unfortunately, this approach suffers from a number of shortcomings. First, because the mechanical correction is not granulated, it is incapable of addressing all of the above-mentioned misalignment contributors. Furthermore, a mechanical correction is limited in its ability to correct for more minor contributors to mis-alignment.